Cancer is a major worldwide public health problem; in the United States alone, approximately 574,000 people died of cancer in 2010. See, e.g., U.S. Mortality Data 2010, National Center for Health Statistics, Centers for Disease Control and Prevention (2010). Many types of cancer have been described in the medical literature. Examples include cancer of blood, bone, skin, lung, colon, breast, prostate, ovary, brain, kidney, bladder, pancreas, and liver, among others. The incidence of cancer continues to climb as the general population ages and as new forms of cancer develop. A continuing need exists for effective therapies to treat subjects with cancer. Breast cancer is one of the most common types of cancer, especially among women. In the United States, it is estimated that there will be about 230,000 new cases of breast cancer and about 40,000 deaths from breast cancer in 2012. See, e.g., Breast Cancer Statistics, National Cancer Institute (2012), available at www.cancer.gov. Among different types of breast cancer, triple negative breast cancer (estrogen receptor (ER)/progesterone receptor/HER-2 negative) is more aggressive than other breast cancer subtypes. No targeted therapy exists for triple negative breast cancer. Triple negative breast cancer has a higher rate of recurrence resulting in death, although the tumors initially appear to respond to chemotherapy. Clearly there is a need to develop effective targeted therapy for triple negative breast cancer.
Changes in protein synthesis are directly linked to multiple human cancers. Translation initiation is deregulated in many cancers, including, e.g., lymphoma, breast cancer, head and neck cancer, colorectal cancer, lung cancer, bladder cancer, cervical cancer, and prostate cancer. Many proteins supporting the high rate of cancer cell growth, proliferation, and survival are translated from mRNAs having secondary structures, which have a greater dependence on rate-limiting translation factors such as eukaryotic initiation factor 4E (eIF4E). eIF4E overexpression in tumors can be a predictor for relapse in breast cancer regardless of nodal status and for drug resistance to adjuvant chemotherapy. A high percentage (>60%) of triple negative breast tumors express high levels of eIF4E. The patient group with high levels of eIF4E has a 1.6-fold higher rate of recurrence and a 2.1-fold increase in relative risk for cancer death. High levels of eIF4E drive the translation of proteins responsible for cancer initiation and progression resulting in aggressive phenotypes and enabling the tumors to better survive radiation treatment and chemotherapy. Therefore, it is desirable to regulate protein translation in cancer, in particular, inhibit the rate-limiting steps in protein translation in order to control cell growth and proliferation.
eIF4E, the rate-limiting factor for eukaryotic protein translation initiation, is ubiquitously expressed in multiple breast cancer cell lines. The activity and availability of eIF4E are controlled, e.g., by binding proteins such as 4E-BP1. The activity of these binding proteins is in turn regulated by phosphorylation, particularly by mTOR. eIF4E over-expression along with the concomitant enhanced translation initiation drives cellular transformation and tumorigenesis. eIF4E is a convergence point for many oncogenic pathways and a key factor for malignancy in human cancer tissues and in experimental cancer models. Enhanced translation initiation is found in malignant breast phenotypes. eIF4E over-expression leads to breast carcinoma angiogenesis and progression. eIF4E elevation of 7-fold or more is a strong independent prognostic indicator for breast cancer relapse and death in retrospective and prospective studies. Antisense oligonucleotide therapy down-regulating eIF4E resulted in a reduction of in vivo tumor growth in PC-3 prostate and MDA-MB-231 breast cancer models in mice. No toxicity was observed when 80% knockdown was observed in essential organs, suggesting tumors are more sensitive to translation initiation inhibition than normal tissue.
Translation initiation factor eIF4E and its binding protein 4E-BP1 are major downstream effectors of the PI3K/Akt/mTOR pathway. mTOR and other members of the PI3K/Akt/mTOR family control the establishment and maintenance of cancer phenotypes. The PI3K/Akt/mTOR pathway has been clinically validated as a target for cancer therapies. Overactivation of PI3K and Akt is found in a wide range of tumor types. PI3K catalyzes the production of phosphatidylinositol-3,4,5-trisphosphate. This lipid activates Akt protein kinase, which in turn triggers a cascade of responses ranging from cell growth and proliferation to survival and motility. PTEN, a dual specificity phosphatase, is an inhibitor of the PI3K pathway. Second to p53, PTEN is most frequently mutated or deleted in human tumors. Several PI3K inhibitors have been developed in clinical trials. mTOR controls translation initiation through phosphorylation and inactivation of 4E-BP binding protein, thereby activating eIF4E. Activation of eIF4E is required for the translation initiation of mRNAs that have long structured ′5-untranslated regions. Increasing evidence suggests that mTOR, as a central regulator of cell growth and proliferation, controls protein biosynthesis. The mTOR pathway controls translation of mRNAs encoding proteins such as cyclin D1, c-Myc, and ornithine decarboxylase that are essential for G1 cell-cycle progression and S-phase initiation. Inhibition of mTOR results in G1 cell cycle arrest. Rapamycin, an mTOR inhibitor, has significant antitumor activity against many tumor cell lines in the NCI screening as well as in humans. However, formulation, solubility and stability issues have hindered the development of rapamycin. Analogs of rapamycin have been developed to address these issues and have shown promising results in Phase II/III clinical trials. There remains a need for alternative cancer therapeutic agents that are effective and safe, e.g., agents having maximum inhibition of tumor growth, minimal toxicity to normal cells, and minimal on-target side effects in the treated subjects.
Excessive and persistent activation of cells characterizes both cancer and fibrotic diseases. Fibrosis is the formation of excess fibrous connective tissue in an organ or tissue in a reparative or reactive process, which can be benign (e.g., wound healing) or pathological. The term fibrosis is often used to indicate a pathological state of excess deposition of connective tissue, which can lead to loss of function and organ failure. During wound healing myofibroblasts are specialized cells that acquire smooth muscle features (including α-smooth muscle actin) and are important contributors to tissue repair. Myofibroblasts can be derived from fibroblasts, epithelial cells, and endothelial cells and are characterized by their ability to secrete extracellular matrix. Regardless of their origin, TGF-β is the principle growth factor responsible for differentiation to the myofibroblast activated phenotype (J L Barnes, Y Gorin, Myofibroblast Differentiation During Fibrosis: Role of NAD(P)H Oxidases, Kidney Int. 2011, 79: 944-956). During normal tissue repair myofibroblasts are activated in a controlled and transient manner (Hinz B. et al., Recent developments in myofibroblast biology: paradigms for connective tissue remodeling, Am J. Pathol. 2012, 180:1340-55). However, excessive and persistent activation of myofibroblasts plays a key role in both fibrotic disease and cancer. In fibrotic disease, large numbers of myofibroblasts accumulate and are responsible for the uncontrolled production of extracellular matrix which leads to loss of function and organ failure. Fibrotic diseases include a variety of clinical entities, including organ specific fibrosis (heart, liver, lung, kidney, bone marrow, skin, pancreas), other forms of fibrosis (retroperitoneal, nephrogenic, and cystic), and connective tissue disorders (atherosclerosis, cirrhosis, scleroderma, keloids, Crohn's disease, and endometriosis). In cancer, the tumor stroma microenvironment contains large numbers of myofibroblasts as well as other cells, which are collectively referred to as cancer associated fibroblasts. Cancer associated fibroblasts play a major role in tumor initiation, progression, and metastais through the production of a variety of growth factors, ECM proteins, and other pro-angiogenic and pro-metastatic factors (Khamis Z I, et al., Active roles of tumor stroma in breast cancer metastasis, Int J Breast Cancer, 2012, 2012:574025).
Therefore, drugs which inhibit the transition of fibroblasts to myofibroblasts have potential for the treatment of cancer, the prevention and treatment of metastatsis, and the treatment of a variety of fibrotic diseases.